<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Alert(警告)框</title>
    <script>
        function myFunction() {
            alert("你好，我是一个警告框！");
        }
    </script>
</head>

<body>
    <input type="button" onclick="myFunction()" value="显示警告框" />
</body>

</html>